Many formulations have been proposed for coating metal and plastic surfaces, including polyepoxy compounds such as the cycloaliphatic diepoxides and glycol ethers. These compounds are generally formulated in solvents or emulsified with water and reacted with typical epoxy hardeners such as epoxy polyamides, polyamines, anhydrides, melamines, imidazoles and acids. However, these formulations pollute the atmosphere since the solvent must be evaporated in order to form a usable coating. The alternative of solvent recovery is found to be uneconomical and therefore not practiced. Water emulsified epoxy coatings also require evaporation which, due to the high heat of water vaporization, is also uneconomical and difficult to drive to completion. To avoid these disadvantages, the use of a solvent free coating formulation comprising a cross-linkable base resin, a cycloaliphatic epoxy compound and a cross-linking initiator has been proposed. Although such a formulation would be acceptable from an economical and environmental standpoint, it is known that the cycloaliphatic epoxy compounds react slowly with the polyepoxy resin resulting in a lack of resistance to common polar solvents such as methyl ethyl ketone, acetone, alcohols, etc. Still further, the polyepoxy compounds produce brittle coatings unless substantial amounts of a flexibilizing agent, such as tripropylene glycol is added to the formulation.
Another deficiency of the above formulated compounds is their inability to accept high levels of pigment loading before an unmanageable viscosity is reached.
Accordingly, it is an object of this invention to overcome the deficiencies of the prior metal and plastic coatings described above.
Another object of this invention is to provide a flexible coating suitable for thin layer application which shows high resistance to chemical solvents.
Still another object of the invention is to provide a formulation which will accept a high level of pigment loading and which possesses good wear resistance for lettering and designs which may have been printed under the coating.